Forget Colorado or Washington — tiny Rhode Island is the marijuana capital of the United States, at least as measured by the percent of state residents who regularly use marijuana.

Map: Marijuana use by state

State-level statistics from the latest National Survey on Drug Use and Health (rather unfortunately acronymed NSDUH) show that just over 1 in 8 Rhode Island residents over age 12 smoke marijuana monthly. This is more than three times the rate in Kansas, where only 4 percent of residents regularly indulge.

Nationally about 7 percent of Americans over age 12 have used marijuana in the past month. Western states tend to have the highest rate of usage, at 9 percent, followed by the Northeast. The South has the lowest overall rate at 5.83 percent.

In what will surely not be a surprise to anyone who has ever been young, 18- to 25-year-olds use marijuana the most. Nearly 19 percent of that group has used marijuana in the past month, according to the NSDUH. But again, the state-to-state variation in those numbers are considerable. More than one third of Vermonters in that age bracket regularly use marijuana, compared to less than 10 percent of Utah's 18- to 25-year-olds.

But usage rates drop off considerably for people age 26 and older: Only 5 percent of Americans in that age group smoke marijuana regularly. Alaska's 26-and-over crowd is the most likely to regularly use marijuana, at 11.18 percent. To put it another way, Alaska's adults are more likely to use marijuana than Utah's college-age crowd.

Both Oregon and Alaska have marijuana legalization measures on their ballots this fall. Not coincidentally, these are the two states with the highest rates of 26-and-over marijuana use.

Legalizing marijuana in Colorado was supposed to help undermine the black market. Instead, it's had almost the opposite effect. PostTV brings you into the world of black market weed dealers to explain. (Gabe Silverman/The Washington Post)